Preparation of fluid catalytic cracking catalysts is generally accomplished by admixing in an aqueous medium particles of zeolites, clay, alumina-containing binder, and a silica source. The produced aqueous slurry is usually subjected to agitation to uniformly disperse the solids within the slurry, and then the slurry is subjected to drying to form essentially water-free solid catalyst particles.
From an efficiency and economy point of view, it is generally preferred to utilize slurries of high solids content. The higher the solids content of the slurry, the less water has to be removed in the drying step, which, on one hand, decreases the fuel consumption of the drying process, and on the other hand, allows the most efficient utilization of the drying equipment. A limiting factor is the slurry viscosity, which, at high solids contents, makes the transfer of the slurry from the mixing vessel to the drying equipment difficult if not impossible. Further, in the case where the slurry is to be subjected to spray-drying in conventional spray-drying equipment utilizing discs or nozzles, high viscosity slurries cannot be efficiently processed. Thus, it was found that in the preparation of fluid catalytic cracking catalysts from aqueous slurries containing zeolites, alumina-containing binders, a clay and a silica source, aqueous slurries of high solids content cannot be readily processed in conventional spray-drying equipment due to the high viscosity. This is particularly true if the alumina-containing binder is an alpha alumina monohydrate derived from the decomposition of aluminum alkoxides with water.
It has now been discovered that if a small, but effective, amount of aluminum hydroxychloride additive, having the general formula of [Al.sub.2 (OH).sub.6-y Cl.sub.y ].sub.x, where x=1 to 6 and y=1 to 2, is incorporated in the aqueous slurry used for the preparation of fluid catalytic cracking catalysts, the viscosity of the slurry can be significantly reduced.
This reduction in slurry viscosity allows the solids content of the slurry to be increased up to the viscosity level the slurry had prior to the incorporation of the additive. This increase in solids content can amount to significant quantities in the neighborhood of up to about 20-30% by weight based on the original solids content of the slurry, which considerably improves the fuel efficiency of the drying step and also allows increased production rates.
Aluminum hydroxychloride has been employed by the prior art as the alumina-containing binder in the preparation of cracking catalysts. Thus, Canadian Pat. No. 967,136 of May 6, 1975 (Lengade, A. T.), describes the use of an aluminum hydroxychloride sol as binder in the preparation of a zeolite-based cracking catalyst. In the process of the aforementioned Canadian patent, the zeolite and clay components of the catalyst are dry mixed, then combined with an alumina-containing sol prepared by the dissolution of aluminum metal with hydrochloric acid. The aqueous alumina sol, containing about 25% by weight Al.sub.2 O.sub.3 and 6.7% chloride as Cl, is used to provide 5-15% by weight alumina binder content (calculated as Al.sub.2 O.sub.3) for the catalyst. After water addition, the sol is admixed with the dry mixed zeolite and clay components to form a slurry of 30% solids content. The slurry is homogenized in a colloidal mill in the presence of a sodium pyrophosphate dispersant, then spray dried. When this relatively large quantity of sol is incorporated in the catalyst mixture, difficulties may arise as far as the end uses of the catalyst are concerned due to a perhaps unacceptably high residual chloride content. These problems are minimized when the aluminum hydroxychloride is used only in small quantities as a viscosity-reducing additive.
The structure of basic aluminum hydroxychloride has been established by nuclear magnetic resonance (NMR) studies and such study was published in the 1981 issue of the Z. anorg. allg. Chem. Volume 483, pages 153-160.